1. Field of the Invention
The present invention relates to an image glazing device for applying a gloss to an image which has been formed on a paper using toner or coloring dye. In this device, the image is subjected to heat, pressure or the like when the gloss is applied thereto.
2. Description of the Prior Art
In a method of forming an image on a paper, a photosensitive member having photoconductivity is electrically charged and exposed to light reflected from an original document so that an electrostatic latent image may be formed thereon. Then, toner is caused to adhere to the electrostatic latent image and transferred onto paper to form a visible toner image thereon.
U.S. Pat. No. 4,399,209 discloses another method in which a photosensitive sheet coated with a large number of microcapsules and an image receiving sheet coated with developing material are used. Each of the microcapsules contains photo-setting material and colorless dye which is colored by the action of the developing material coated on the image receiving sheet. When the photosensitive sheet is exposed to light reflected from an original document, the microcapsules coated thereon are partially hardened to selectively form a hardened image. The image receiving sheet is then overlapped on the photosensitive sheet and subjected to pressure so that unhardened microcapsules may be crushed. In this situation, the colorless dye which flows out of the crushed microcapsules is colored by the developing material of the image receiving sheet to form a colored image. U.S. Pat. No. 4,576,891 discloses such a coloring reaction.
FIGS. 1a and 1b depict a known heating device for heating the image receiving sheet having thereon such a toner or colored image. The device of FIG. 1a is an oven type one in which a paper placed on a transport means 1 is indirectly heated by a plurality of heaters 2 disposed above the transport means 1. The device of FIG. 1b is a contact type one which is provided with a heat roller 3 and a pressure roller 4. The heat roller 3 accommodates a halogen lamp or the like as a heating means. The pressure roller 4 applies pressure to the image receiving sheet supplied between it and the heat roller 3.
In the method of utilizing the photosensitive member with photoconductivity, heating the paper having the toner image thereon softens the thermoplastic resin contained in the toner and fixes the toner.
In the method disclosed in U.S. Pat. No. 4,399,209, heating the image receiving sheet having thereon the colored image expedites the coloring reaction of the colorless dye, resulting in a desirable image. This fact is disclosed in U.S. Pat. No. 4,576,891. Furthermore, as disclosed in U.S. Pat. No. 4,554,235, if thermoplastic pigment is coated on the image receiving sheet, the use of the aforementioned heating device can soften the thermoplastic pigment to add a gloss to the colored image.
However, the device of FIG. 1a employing the indirect heating means can not satisfactorily smooth the thermoplastic resin or pigment. Therefore, this device can not produce a high gloss image. Besides, the relatively low efficiency of the heating means causes the device to be formed undesirably into a large size. Moreover, the paper tends to be slightly curled by the heating and is occasionally brought into contact with one of the heaters. This fact causes the paper to be scorched or set on fire.
In the device of FIG. 1b, the thermoplastic resin or pigment softened by the heating is occasionally caused to adhere to the heat roller and causes an unintentional transfer thereof called "offset". In other words, the thermoplastic resin or pigment adhering to the heat roller is then transferred onto the paper in the subsequent image forming process, thus occasionally spoiling the next image. To prevent this, heat roller requires a relatively large cleaning device, resulting disadvantageously in a large-sized heating device.